Metal-clad three-conductor high-voltage transmission line

ABSTRACT

The three conductors of the high voltage transmission line are arranged in triangular array within the metal-clad casing and are supported at longitudinally spaced apart points. At each support point, three insulator bodies are provided so that each conductor is supported by a single insulator body. Each insulator body surrounds one conductor, at least partially, and is attached at two points of the metal casing which are separated from each other by at least an angle of 90* relative to the periphery of the casing.

United States Patent [191 Hoffmann METAL-CLAD THREE-CONDUCTORHIGH-VOLTAGE TRANSMISSION LINE Fritz Hoffmann, Rheinheim, GermanySiemens Aktiengesellschaft, Munich,

' Germany Filed: Mar. 27, 1972 Appl. No.: 238,405

[75] Inventor:

[73] Assignee:

Foreign Application Priority Data Apr. 8, 1971 Germany ..I...-P 21 18176.0

[52] US. Cl. 174/99 B, 174/16 B, 174/24, 174/149 B Int. Cl....; 1101b9/06,'H01b 17/18 Field of Search 174/99 R, 99 B, 16 B,

174/16R, 24, 27,15 C, 149 B References Cited UNITED STATES PATENTS3,349,168 10/1967 Rehder et al 174/99 B 51 Aug. '7, 1973 1,851,9393/1932 Williams 174/99 R 3,164,667 1/1965 Frowein 174/27 I FOREIGNPATENTS OR APPLICATIONS 1,448,008 6/1966 France 174/99 B 1,109,3774/1968 Great Britain 174/99 B Primary Examiner-Bernard. GilheanyAssistant Examiner- A. T. Grimley Attorney-Hugh A. Chapin [57] vABSTRACTThe three conductors of the high voltage transmission line are arrangedin triangular array within the metalclad casing and are supported atlongitudinally spaced apart points. At each support point, threeinsulator bodies are provided so that each conductor is supported by asingle insulator body. Each insulator body surrounds one conductor, atleast partially, and is attached at two points of the metal casing whichare separated from each other by at least an angle of 90 relative to theperiphery of the casing.

14 Claims, 3 Drawing Figures PAIENTEU ABE U WEI 1 [1F 3 METAIi-CLADTHREE-CONDUCTOR, HIGH-VOLTAGE TRANSMISSION LINE FIELD F THE INVENTIONThe invention relatesto inetal-clad three conductor high voltagetransmission lines, and more particularly,

BACKGROUND THE INVE TION Heretofore, three-conductor high-voltagetransmission lines have been knowii 'to havecylindrical metalcladcasings, or the like encapsulation, in which three, preferably tubular,high-voltage conductors are arranged at the corners of a'triangle. Inmost cases, these high-voltage transmission lines have been constructedwith pressurized-gas insulation. In addition, these lines can functionparticularly as a three-conductor bus bar system in which case,'branchlines are brought out from the cylindrical casing at regular, relativelyclose intervals. I u

. In order to' orient the conductors within the casing, variousstructures have been used. For example, ina three-phase bus bar systemknown from the German published Patent Application No. 1,194,026, thehighvoltageconductors have been mounted in a symmetrical arrangement bysupport insulators which engage each high voltage conductor on twosides. These support insulators have each been attached at the endretion between the conductor and the support insulator.

Moreover, the partitions and attachment means can affect the dielectricstrength so that use at very high voltages, for instance, of 110kilovolts (kV) may not be possible. i l a High-voltage lines have alsobeen known in which the high voltage conductors 'are held in place byringshaped bodies of insulating material which are common for all threeconductors and are, attached unilaterally to the casing. However, inthese cases, the leakage paths have been so short as to create apossibility of phase short circuits occurring. I

Accordingly, it is an object of the invention to reduce the costrequired for a three-conductor high-voltage transmission line withoutsacrificing dielectric strength.

It is another object of the invention to provide a highvoltagetransmission line which is mechanically sufficiently strong to withstandparticularly the electrodynamic forces in the case of a short circuit.

SUMMARY OF THE INVENTION and is attached at the ends to two points ofthe metal casing so as to be disposed in chordal fashion relative to thecross-section of the casing which are separated from each other at leastby an angle'of 90 at the circumference of the casing.

As the insulating bodies are attached only at the casing there is noneed of any partitions, arranged in starfashion. Further, as the leakageand breakdown paths at thev insulator body are relatively long due tothe fact that the attachment points are displaced by at least an angleof 90 at the circumference of the casing, the dielectric strength of themounting arrangement is adequate. In this respect, it is noted thatthese paths are longer than in arrangements where the high-voltageconductors are supported by support insulators which extend radiallytoward the axis of the casing. Also, in contrast to transmission lineswhich utilize ring-shaped bodies of insulating material, the danger ofphase short circuits due to leakage paths is substantially reduced, asthe paths along the .surfaces of the insulating material between thephase conductors are about twice as long. 7

According to the invention, symmetrical arrangements are preferablychosen in which all insulator bodies are identical. In one embodiment,the insulator bodies are attached at the metal casing by a fasteningmeans which is common to two respective insulator bodies and at pointsdisplaced -.by an angle of 120 at the circumference. The fastening meansis, for example, in the form of a screw which secures two adjacentinsulator bodies against a projection which is situated between theinsulator bodies and is connected with the casing. The projection can bean integral portion of the casing.

Altematively, an elastic connection can be used to secure the insulatorbodies to the casing. To this end, a rubber member which isadvantageously made more or less conductive by the addition of graphiteor silicon carbide (SiC), is disposed between two adjacent insulatorbodies so as to be deformed against the inside .of the casing when theinsulator bodies are screwed together.

. Similar fastening means can also-be. provided in the vicinity of thehigh-voltage conductor, so that a vibration-damping, resilient butsufficiently secure attachment is obtained. I

The insulator bodies are preferablyconstructed in a symmetrical fashionwith two arms curved in the same sense as the metal casing. Such acurvature results in an increase of the leakage path, as will beexplained in further detail below. Particularly advantageous areinsulator bodies which are shaped in the cross-section perpendicular tothe longitudinal axis of the high-voltage conductors. In this way, highstrength can be obtained with a low expenditure for material. Theinsulator bodies can also have cutouts over most of .the cross sectionand, in such a case, it is'adviseable to connect the legs surroundingthe cutouts inthe vicinity of the highvoltage conductor so as to form aring for enclosing the conductor. The ring can then provide thereinforcement necessary for a clamping connection. At the other end,i.e. in the vicinity of the attachment point at the casing,a-reinforcement can be obtained by making the height of the crosssection of the insulator body decrease from the high-voltage conductortoward the attachment point in such a'manner that the legs merge intoeach other at the attachment point. .A freesupported beam or simple beamis thus obtained with an approximately uniform distribution of thelargest mechanical stresses. I I

These and other objects and advantages of the invention will become moreapparent from the following detailed description and appended claimstaken in conjunction with the accompanying drawings in which:

DESCRIPTION JFTI-IE DRAWINGS DESCRIPTION OFTl-IE PREFERRED EMBODIMENTReferring to FIGS. 1 and 2, the three-conductor highvoltage transmissionline for carrying, for example 1 l kilovolts (kV), can be part of apressurized gasinsulated high voltage switching station. For-example,the line can be the bus bar of a three-phase system.

Referring to FIG. 1, the transmission line includes a cylindrical metalcasing 1 which is at ground potential.

- The casing 1 serves to encapsulate three high-voltage conductors 2, 3and 4 at the corners of an isosceles triangle with respect to thelongitudinal axis of the casing 1. In. addition, a number of alignedcylindrical T- connectors 5, each of which is used to enclose a branchconductor 6 for each conductor 2, 3, 4 are disposed in spacedlongitudinal relation along the casing l. The

high-voltage conductors 2-6, are aluminum or copper tubes, while thecasing l is of steel, as is customary.

The high-voltage conductors 2, 3, 4 are supported within the casing l bythree insulator bodies 8, which are disposed in a plane perpendicular tothe axis of the casing 1 to define an empty triangular space. Theinsulator bodies 8 are of one-piece construction and have a shaped crosssection as shown. Each body 8 which centrally supports a conductor 2, 3,4 has two arms 7, 9 which surround a high-voltage conductor 2, 3, 4 andare shaped to define an annular reinforcement 10 about the conductor.The annular reinforcement 10 also serves to connect the inner and outerlegs 11 and v 12 of the profile of the body 8. As shown, the legs l1,

12 have a curvature which corresponds to that of the ,casing l, with twoouter arcuate portions 13 and 14 having a larger diameter than the twoinner arcuate portions 15 and 16. In this way, the cross-section heightdecreases from the high voltage conductor toward the casing 1 so thatthe legs 1 l and 12 converge at the ends.

The arcuate portions l3, l5 and 14, 16 of each insulator body 8 areconnected at about the center of the arms 7, 9 by two webs 19, 20, whilethe larger crosssectional part of the body 8 in between is constitutedby cutouts 21. The insulator bodies 8 are therefore light-weight, butmechanically strong structures, which are shaped largely as beams ofconstant tensional stress. Upon stratification of solid 'and gaseousinsulating materials in the direction of the electric field, the cutouts21 also allow the gases to be stressed only slightly, so that glowdischarges do not occur.

Referring to FIG. 2, for purposes of clarity, the mannet in which eachconductor 2, 3, 4 is mounted in an insulator body 8 will be explained byreference to the tween the body 8 and conductor 4. The rubber ring 6 isfitted into a recess of the body 8 against a shoulder 18 and iscompressed by a ring of insulating material 17, which is pushed againstthe shoulder 18 by means of suitable screws. In some cases, the ring 17may also be equipped withvexternal thread and screwed into a threadedhole formed in the body 8. A deformable resilient attachment of theinsulator body 8 to the conductor 4 is thus obtained.

The manner in which each insulator body 8 is secured to the casing 1will be explained for clarity by reference to one point of attachment.As shown, each insulator body 8 is provided with a recess 22 at theattachment point to the casing l as well as with a projection 13. Therecess 22 and projection 23 of each adjacent insulator body 8 are sizedso as to mate with a corresponding projection and recess, respectively,so that two such insulator bodies overlap at the common attachmentpoint. In addition, each body 8 has a further recess which cooperateswith the adjacent recess of the adjacent body to form a groove 24 inwhich a deformable rubber member 25 is positioned in facing relation tothe casing 1. A screw 26 passes through the area of overlap of the twoadjacent bodies 8 and serves to secure each together while deforming therubber member 25 against the casing l. The deformed rubber member 25thus acts as a projection of the casing 1. In this way, the high-voltageconductors are secured with respect to the casing 1 elastically, butwithout play.

Referring to FIG. 2, the respective insulator bodies 8 of each supportpoint are shown displaced with respect to the axis of each adjacent Tconnector 5 in the longitudinal direction of the casing 1. This ispossible, in spite of the current forces emananting from the branchconductor 6, because the insulator bodies 8 are mechanically stableparts. They can be manufactured simply by a casting or molding process.Due to their arcshaped construction which is matched to the wall of thecasing, and the attachment points which are staggered at thecircumference, the insulator bodies 8 further present such longsurface-leakage paths between'the high-voltage conductors 2, 3, 4 andthe casing 1 that the operating and test'voltages can be substantiallyincreased over arrangements with support insulators which are disposedradially with respect to the axis of the encapsulation structure.

As the insulator bodies require no machining of the conductors or of thecasing at the points of attachment, the bodies can be arranged at anydesired spacing along the casing.

Referring to' FIG. 3, wherein like reference characters indicate likeparts as above, the transmission line is provided with a cylindricalcasing l in which the conductors 2, 3, 4 are positioned at the cornersof an equilateral triangle. The conductors 2, 3, 4 are supported in thecasing 1 by three insulating bodies 8 of identical and symmetricalconstruction. These bodies 8 are similar to the above described bodiesand are connected to the casing 1 at points space apart relative to theperiphery of the casing 1.

What is claimed is:

I. In combination with a transmission line having a casing and threehigh-voltage conductors disposed in a parallel triangular array withinsaid casing; a plurality of insulator bodies each individually mountinga respective one of said conductors within said casing, each saidinsulator body surrounding a respective one of said conductors at leastpartially and being attached at two spaced apart points to said casing,said points being circumferentially spaced at an angle of at least 90from each other.

2. The combination as set forth in claim 1 wherein said insulator bodiesare each of identical construction.

3. The combination as set forth in claim 1 wherein said points arecircumferentially spaced at an angle of 120 from each other and whichfurther includes means at each said point for fastening two adjacentinsulator bodiesin common to said casing. I

4. The combination as set forth in claim 3 wherein said fastening meansincludes an inwardly directed projection on said casing and a screwpassing through two adjacent insulator bodies and pressing said twobodies against said projection.

5. The combination as set forth in claim 4 wherein said projection is anelastically deformable member disposed between said two bodies. 6. Thecombination as set forth in claim I wherein said casing is ofcylindrical cross-sectional shape and each insulator body has a pair ofsymmetrically disposed arms curved in the same sense as said casing toprovide a long surface-leakage path between a respective conductor andsaid casing.

7. The combination as set forth in claim 1 wherein each insulator bodyis predominantly shaped in a crosssection perpendicular to alongitudinal axis of said casmg.

8. The combination as set forth in claim 1 wherein each insulator bodyincludes a plurality of cut-outs in a major part of said cross-section.

9. The combination as set forth in claim 8 wherein each insulator bodyhas a pair of legs defining said cutouts and a ring enclosing arespective one of said conv 6 ductors therein.

10. The combinationas set forth in claim 1 wherein each insulator bodyis. of decreasing cross-sectional height from a point surrounding arespective conductor towards each said point of attachment to obtain anapproximately uniform distribution of stresses. v

11. In combination with a transmission line having a casing ofcylindrical cross-sectional shape and three high-voltage conductorsdisposed in a parallel triangular array within said casing; a pluralityof insulator bodies mounting said conductors within said casing, eachsaid insulator body surrounding a respective one of said conductors atleast partially centrally thereof and being attached at two spaced apartpoints to said casing, said points being circumferentially .spaced at anangle of at least from each other, each said insulator body having apair of symmetrically disposed arms curved in the same sense as saidcasing.

12. The combination as set forth in claim 11 wherein each I insulatorbody is of decreasing cross-sectional height from a respective conductortowards each said point. v

13. The combination as set forth in claim 11 wherein each insulatorbodyis of one-piececonstruction.

14. In combination with a three-phase high-voltage transmission linehaving a casing and three high-voltage conductors disposed in a paralleltriangular array within said casing; a plurality of insulator bodieseach body individually mounting a respective one of said conductorscentrally thereof within said casing and being secured at opposite endsto said casing in chordal fashion relative to the cross-section of saidcasing, said bodies defining an empty triangular space.

2. The combination as set forth in claim 1 wherein said insulator bodies are each of identical construction.
 3. The combination as set forth in claim 1 wherein said points are circumferentially spaced at an angle of 120* from each other and which further includes means at each said point for fastening two adjacent insulator bodies in common to said casing.
 4. The combination as set forth in claim 3 wherein said fastening means includes an inwardly directed projection on said casing and a screw passing through two adjacent insulator bodies and pressing said two bodies against said projection.
 5. The combination as set forth in claim 4 wherein said projection is an elastically deformable member disposed between said two bodies.
 6. The combination as set forth in claim 1 wherein said casing is of cylindrical cross-sectional shape and each insulator body has a pair of symmetrically disposed arms curved in the same sense as said casing to provide a long surface-leakage path between a respective conductor and said casing.
 7. The combination as set forth in claim 1 wherein each insulator body is predominantly shaped in a cross-section perpendicular to a longitudinal axis of said casing.
 8. The combination as set forth in claim 1 wherein each insulator body includes a plurality of cut-outs in a major part of said cross-section.
 9. The combination as set forth in claim 8 wherein each insulator body has a pair of legs defining said cut-outs and a ring enclosing a respective one of said conductors therein.
 10. The combination as set forth in claim 1 wherein each insulator body is of decreasing cross-sectional height from a point surrounding a respective conductor towards each said point of attachment to obtain an approximately uniform distribution of stresses.
 11. In combination with a transmission line having a casing of cylindrical cross-sectional shape and three high-voltage conductors disposed in a parallel triangular array within said casing; a plurality of insulator bodies mounting said conductors within said casing, each said insulator body surrounding a respective one of said conductors at least partially centrally thereof and being attached at two spaced apart points to said casing, said points being circumferentially spaced at an angle of at least 90* from each other, each said insulator body having a pair of symmetrically disposed arms curved in the same sense as said casing.
 12. The combination as set forth in claim 11 wherein each insulator body is of decreasing cross-sectional height from a respective conductor towards each said point.
 13. The combination as set forth in claim 11 wherein each insulator body is of one-piece construction.
 14. In combination with a three-phase high-voltage transmission line having a casing and three high-voltage conductors disposed in a parallel triangular array within said casing; a plurality of insulator bodies each body individually mounting a respective one of said conductors centrally thereof within said casing and being secured at opposite ends to said casing in chordal fashion relative to the cross-section of said casing, said bodies defining an empty triangular space. 